Method of controlling lost circulation

ABSTRACT

This specification discloses a method of controlling lost circulation in drilling operations. In carrying out the method of the invention, an aqueous mixture of a dispersing agent and a water dispersible oleophilic colloid is introduced into the well. This aqueous mixture is circulated down the well and into the vicinity of a formation into which lost circulation is occurring. The aqueous mixture is there mixed with an oleaginous liquid and a gel is formed which tends to plug the formation into which lost circulation is occurring. The oleophilic colloid may be a normally water swellable clay such as bentonite which has been treated to render it oleophilic. The oleaginous liquid may comprise an oil-base drilling fluid utilized in drilling of the well.

United States Patent 1191 Kelly, Jr. 14 1 Apr. 3, 1973 [54] METHOD OFCONTROLLING LOST 3,448,800 6/1969 Parker et a1. ..175/72 x CIRCULATION3,461,980 8/1969 Kelly, Jr. [75] Inventor: John Kelly Jr. Arlington Tex3,467,208 9/1969 Kelly, Jr ..l75/72 [7 3] Assignee: Mobil OilCorporation Primary Examiner stephen Novosad Attorney-William J.Scherback et a1. [22] Filed: Nov. 12, 1971 21 Appl. 190.; 198,247ABSTRACT This specification discloses a method of controlling 52 U.S. c1..175 72, 166/294 19st circulation in drilling operations 19 carryingout 51 n CL 21 21 04, 211, 33 13 21 43 00 the method of the invention,an aqueous mixture of a 53 pi f Search 175/72 70 65; 1 /292 294dispersing agent and a water dispersible oleophilic col- 165/293 300;252/35 LC loid is introduced into the well. This aqueous mixture iscirculated down the well and into the vicinity of a 5 R f n Ci formationinto which lost circulation is occurring. The aqueous mixture is theremixed with an oleaginous UNITED STATES PATENTS liquid and a gel isformed which tends to plug the for- 2 531,812 11 1950 HauserMQ ..252/8.5nation which lost circulation is curring- The 2:637692 5/l953 Nahin"252/85 oleophilic colloid may be'a normally water swellable 2,675,3534/1954 Dawson ....252/s.5 clay Such as bemonite which has been treatedto 2,776,713 1/1957 Mor an 1 1 165/293 render it oleophilic. Theoleaginous liquid may com- 2,800,964 7/ 1957 Garrick ...l66/293 X prisean oil-base drilling fluid utilized in drilling of the 2,990,016 6/1961Goins, Jr. et a1. 166/293 welL 1 3,070,179 12/1962 Moore ..175/723,411,581 1 11/1968 Alpha ..175/72 X 9 Claims, N0 Drawings METHOD OFCONTROLLING LOST CIRCULATION BACKGROUND OF THE INVENTION This inventionrelates to the drilling of wells into the earth's crust and moreparticularly to a new and improved method of lost circulation control insuch drilling operations.

Typically, wells are extended into the earth s crust to desiredsubterranean locations, e.g. hydrocarbon-bearing formations, through theapplication of rotary drilling techniques. In the rotary drilling of awell, a drilling fluid is circulated through the well in order to removethe cuttings therefrom. The drilling fluid may be gaseous or liquid,although in most rotary drilling procedures, the drilling fluidcomprises a suitable liquid either alone or in the form of a mud, Le, aliquid medium having solids suspended therein. The drilling fluid maycomprise either an aqueous-base or an oil-base liquid medium. The liquidmedium used in an oil-base drilling fluid may be a relatively pureoleaginous liquid such as crude petroleum oil or diesel oil, or it maybe an inverted emulsion, i.e., a water-in-oil emulsion, in which oilforms a continuous phase. Such oil-base fluids may be used to advantagewhere the formation being drilled is a suspended oil or gas producer, orwhere unstable shale formations are encountered. In an aqueous-basedrilling fluid, the liquid medium typically is fresh water, salt water,or an oil-in-water emulsion in which the water is the continuous phase.Where practical, it usually is desirable for reasons of economy to usean aqueous-base drilling fluid throughout much of the drillingoperation.

The suspended solids in an aqueous-base drilling mud typically take theform of clays of the kaolinite, montmorillonite, or illite groups. Suchclays are utilized to impart desirable thixotropic properties to thedrilling mud and also serve to coat the walls of the well with arelatively impermeable sheath commonly termed a filter cake whichretards the loss of fluid from the well into the formations penetratedby the well. Exemplary of the clays which may be utilized inaqueous-base drilling muds is bentonite, which is a montmorillonitetypeclay. Bentonite is dispersed within the aqueousbase liquid as colloidalparticles and imparts various degrees of thixotropy to the mud. Clays,such as those described above which have been rendered oleophilic bysuitable treatment, maybe used in oil-base drilling fluids. For example,the Bentones which are formed by treating bentonites with lone-chainamines are thickening agents which are widely used in oil-base drillingfluids. Other material such as lamp black and blown asphalt may also beused as viscosifiers in oil-base drilling fluids.

In addition to various clays such as mentionedabove, a drilling fluidalso may contain one or more weighting agents which function to.increase the density of the fluid such that it will offset highpressures which may be encountered during the drilling operation.Examples of weighting agents which may be used in either aqueousbase oroil-base fluids are heavy minerals such as barite (barium sulfate) andgalena (lead sulfide).

One difflculty which is often encountered in drilling operations isflost circulation" which involves a loss of unacceptably large amountsof drilling fluid'into a formation penetrated by the well. Such aformation is commonly termed a lost circulation zone. Lost circu- LIIlation may occur when the well encounters a formation of unusually highpermeability or one which has naturally occurring fractures or fissures.Also, a formation may be fractured by the hydrostatic pressure of thedrilling fluid, particularly when a changeover is made to a relativelyheavy mud in order to control high formation pressures.

Numerous techniques have been developed in order to control lostcirculation. One common expedient is to increase the viscosity of thedrilling fluid in order to increase its resistance to flow into theformation. Another technique involves the addition of bulk material,such as cottonseed hulls, sawdust, or ground walnut shells to thedrilling fluid. Also, it has been proposed to place a soft plug" such asa gel formed by a liquid'clay dispersion into the lost circulation zone.For example, as disclosed in U.S. Pat. No. 2,800,964 to Garrick, a gelmay be formed within the well by mixing an aqueous liquid and an oildispersion of a hydrophilic clay, and the gel forced into the lostcirculation zone. In another procedure, a hydraulic cement slurry may beplaced in the lost circulation zone and allowed to set.

My invention disclosed .in U.S. Pat. No. 3,467,208 is directed to amethod of controlling lost circulation in drilling operations. Anaqueous suspension of an oleophilic colloid which is both water and oildispersible is introduced intoa drill string which extends into a well.The aqueous suspension is circulated through the drill string and intothe wellbore where: it is contacted with an oleaginous liquid to form agel which tends to plug the formation into which lost circulationoccurs.

SUMMARY OF THE INVENTION The present invention is directed to animprovement to my aforementioned U.S. Pat. No. 3,467,208. Thisimprovement concerns the inclusion of a dispersing agent in the aqueoussuspension of an oleophilic colloid thereby allowing an increased amountof oleophilic colloid to be employed. Thus, in accordance with thisinvention there is provided a method of alleviating fluid loss into asubterranean formation penetrated in the drilling of a well thereinto.An aqueousmixture of a dispersing agent and a water dispersibleoleophilic colloid which acts as an oleaginous gelling agent-isintroduced into the well. This aqueous mixture is circulated down thewell and into the vicinity of the formation and is there mixed with anoleaginous liquid. The oleophilic colloid is thereby dispersed into theoleaginous liquid and forms a gel which tends to plug the formation andmitigate the fluid loss thereinto.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The gelling agent used incarrying out the present invention may be any suitable oleophiliccolloid which is both water and oil dispersible and which exhibits goodgelling action in an oleaginous liquid while exhibiting relativelylittle or no gelling action in an aqueous liquid. Particularly suitablefor use in the present invention are the normally water swellable clayswhich have undergone treatment to render them oleophilic. Exemplary ofsuitable oleophilic clays are the bentonites or other clays which havebeen treated with an oil-wetting surfactant such as a long-chainquaternary .or

nonquaternary amine. For a more detailed description of such clays andtheir method of preparation, reference is made to CHEMICAL ENGINEERING,March 1952, pp. 226-230; US. Pat. No. 2,531,812 to I-lauser; and US.Pat. No. 2,675,353 to Dawson. Suitable oleophilic clays also may beprepared by dehydrating a hydrophilic clay such as bentonite, and thentreating the dehydrated clay with a glycol or glycol ether. For a moredetailed description of this procedure, reference is made to U.S. Pat.No. 2,637,692 to Nahin. Suitable olephilic colloids are available underthe trade names of Geltone and Petrotone.

The dispersing agent employed in carrying out the present invention maybe any suitable material which functions to promote and maintainseparation of the individual, extremely fine particles of solid whichare usually of colloidal size. As will be recognized by those skilled inthe art, various such dispersing agents are conventionally employed indrilling muds in order to maintain adequate dispersion of clays added toimpart desired rheological properties to such muds. Also, as will berecognized by those skilled in the art certain dispersing agents aremore effective in alkaline environments and therefore it is desirable toadjust the pH of the liquid medium into which the dispersing agent isadded to an alkaline pH. The pH may be adjusted, for example, by addingcaustic soda to the liquid medium. Examples of dispersing agents whichmay be used are lignites, chrome lignosulfonates, other lignosulfonatessuch as iron, nickel, and cobalt lignosulfonates, tannins, and complexphosphates such as polyphosphates and pyrophosphates. Dispersing agentswhich have been found to give particularly good results when used inaccordance with this invention and which are therefore preferred arechrome lignosulfonates and ferrochrome lignosulfonates.

In rotary drilling there is employed a drill string which carries on itslower end a drill bit having one or more openings for the passage ofdrilling mud between the drill string and the well. The drill stringextends through a rotary table on the floor of the drilling rig and issupported by the rig through the means of a drawworks system. Typically,the drilling mud is withdrawn from a mud pit near the surface of thewell and passed into the drill string via a rotary swivel. The drillingmud is pumped downwardly through the drill string and outwardly into thewell through the openings in the drill bit. The mud is then pumped tothe surface of the earth through the annulus between the drill stringand the wall of the well. At the surface the mud may be passed through asuitable separation zone where drill cuttings and other entrained solidsmay be separated and thence passed to the mud pits for reintroductioninto the drill string. So-called reverse circulation" drilling may alsobe employed wherein the drilling mud is pumped down the well through theannulus between the drill string and the wall of the well and thencethrough the openings in the bit and up the drill string to the surfaceof the earth.

The invention normally will be used most advantageously in conjunctionwith a drilling procedure employing an oil-base drilling fluid, whichdrilling fluid is pumped downward through the drill string and upward tothe surface of the earth through the annulus. Accordingly, thisinvention is described primarily with reference to such a procedure.

loid. For example, as disclosed in copending application Ser. No.198,357, entitled TECHNIQUE FOR CONTROLLING LOST CIRCULATION, by JosephU. Messenger, filed of even date, the aqueous mixture may include inertparticulate materials such as barite, gilsonite, silica, and calciumcarbonate. Thereafter, the drilling fluid is again introduced into thedrill string and the aqueous slug is. entrained within the column ofdrilling fluid and circulated down the drill string and thence into thewell through the outlet ports of the drill bit. As the aqueous mixtureenters the well it is mixed with the oleaginous liquid provided by theoil-base drilling fluid and reacts with this liquid to form a gel.

In accordance with an embodiment of this invention, a pumpable aqueousmixture of a dispersing agent and a water dispersible oleophilic colloidwhich acts as an oleaginous gelling agent is formed by adding thedispersing agent to the water prior to or concomitantlywith the additionof the oleophilic colloid thereto. The addition of the dispersing agentto the water enables the addition of an increased amount of oleophiliccolloid to the water while maintaining a pumpable slurry, that is, aslurry which has a viscosity sufficiently low that it may be circulatedwithin the well. The addition of the dispersing agent to the water priorto or concomitantly with the addition of the oleophilic colloid theretofacilitates the forming of a pumpable aqueous mixture containing anincreased amount of oleophilic colloid.

The amount of dispersing agent employed in carrying out this inventionis that amount which will allow a sufficient amount of oleophiliccolloid to be dispersedin water but less than that amount which willreduce the efficiency of the gelling action when the aqueous mixturecontaining the oleophilic colloid is mixed with an oleaginous liquid.The specific amount of any selected dispersing agent to be employed mayreadily be determined by straightforward tests wherein various amountsof dispersing agent and oleophilic colloids are mixed together to form apumpable slurry which will gel when mixed with an oleaginous liquid. Atypical formulation for use in controlling lost circulation is obtainedby forming a slurry comprised of the following materials inapproximately the concentrations specified: water 350 cubic centimeters,ferrochrome lignosulfonates 4.6 grams, caustic soda'-- 2.3 grams, and anoleophilic colloid available under the trade name of Geltone 350 grams.

Ideally, the drill bit will be located adjacent the lost circulationzone so that as the gel is forming, it is displaced immediately into thelost circulation zone where the gelling reaction continues until a stiffplug is formed, thus sealing the lost circulation zone. However, in manycases, the precise depth of thelost circulation zone will be unknown. Insuch cases, it is important to maintain circulation of the drillingfluid in order to ensure that the plug that is formed by mixing theoleaginous liquid with the aqueous mixture of a dispersing agent and awater dispersible oleophilic colloid is forced into the lost circulationzone. Due to its thixotropic character, this plug will tend to stiffenafter it is displaced into the formation where it is subject to lowershear stresses than while circulated within the well;

It is contemplated that in most cases, adequate contact between theaqueous mixture of the dispersing agent and colloid and the oleaginousliquid can be obtained simply by passing the mixture through the outletports of the drill bit into the well. However, if more intimate mixingis desired, the drill string may be withdrawn from the well and equippedwith a mixing sub such as that described in U.S. Pat. No. 2,800,964.Thereafter, the drill string may be reinserted within the well and theaqueous mixture introduced as described above.

If desired, a suitable oleaginous liquid, such as the oil-base drillingfluid used during normal operations, may be pumped down the well annulusin conjunction with circulation of the aqueous mixture through the drillstring. These steps should be correlated such that fluid is beingpumped'into the annulus as the aqueous mixture is displaced from thedrill string into the well. This will further promote mixing of theaqueous mixture and the oleaginous liquid and will provide a continuoussupply of oleaginous liquid to the mixing zone.

By'introducing the aqueous mixture of dispersing agent and oleophiliccolloid into the drill string as a discrete slug, the possibility ofsignificant contact between the oleophilic colloid and the oil-basedrilling fluid within the drill string is substantially reduced. Thus,the tendency of the oleophilic colloid to go into an oleaginousdispersion within the drill string is reduced with the result that thereis little chance of forming a stiff gel within the drill string.

In order to further ensure against the oleophilic colloid within theaqueous mixture contacting the oil-base drilling fluid within the drillstring, it is preferred in carrying out the invention to immediatelyprecede the aqueous mixture with a liquid buffer system comprising anaqueous liquid such as fresh water, brine, or if desired, anaqueous-base drilling fluid having hydrophilic clays dispersed therein.The buffer system normally will comprise a relatively small amount,e.g., on the order of one-half to five barrels, depending upon the depthto the end of the drill string which typically may vary from about 1,000to 25,000 feet. A large amount of the liquid buffer system normallyshould be avoided in order to ensure that contact of the aqueous mixtureof dispersing agent and the oleophilic colloid and the oil-base drillingfluid will take place after the aqueous mixture enters the well from thedrill string. The aqueous buffer liquid should, of course, besubstantially free of oleophilic colloids.

It also will be desired in many cases to introduce a second buffersystem into the drill string immediately following the aqueoussuspension of oleophilic colloid. This buffer system, which may beidentical to the firstinjected buffer system, is utilized in order toreduce the possibility of contact within the drill string between theaqueous suspension of oleophilic colloid and the subsequently introducedoil-base drilling fluid.

Where the oil-base drilling fluid is an inverted emulsion, it usuallywill be desirable to utilize as the buffer system an aqueous liquid asdescribed above which is preceded by a substantially water-freeoleaginous liquid such as diesel oil, crude oil, etc. The oleaginousbuffer liquid is employed in this instance primarily for the purpose ofpreventing direct contact within the drill pipe between the aqueousbuffer liquid and the inverted emulsion which may cause the emulsion torevert to an oil-in-water emulsion. A second buffer system comprising aslug of aqueous buffer liquid followed by a slug of oleaginous bufferliquid may be introduced into the drill string immediately following theaqueous mixture of dispersing agent and oleophilic colloid. The amountof oleaginous liquid used in such buffer systems may be relativelysmall, e.g., on the order of one-half to two and one-half barrels,depending upon the depth of the well.

When drilling with an aqueous-base drilling fluid, a procedure similarto that described above may be carried out when lost circulation occurs.In this case, introduction of the aqueous-base drilling fluid into thedrill string is suspended and an aqueous mixture of a dispersing agentand an oleophilic colloid is introduced into the drill string andcirculated downwardly therethrough and into the wellbore. Precedingand/or following the aqueous mixture, an oleaginous liquid such asdiesel oil, crude oil, etc., is introduced into the drill string. Thisoleaginous liquid is introduced for the purpose of mixing with theoleophilic colloid within the wellbore and forming a gel. A sufficientamount of oleaginous liquid for this purpose should be introduced intothe drill string. For example, it-usually will be desirable to introduceat least five barrels of oleaginous liquid. Preferably, the oleaginousliquid is introduced into the drill string ahead of the aqueous mixturesuch that it will be present within the well when the aqueous mixtureenters the well from the drill string. Also, it usually will bedesirable to introduce a buffer system of an aqueous liquid into thedrill string between the oleaginous liquid and the aqueous mixture. Thisbuffer liquid functions similarly as described above in order to preventpremature contact between the aqueous mixture and the oleaginous liquid.

Laboratory tests carried out in accordance with this invention haveshown that the addition of a dispersing agent into water prior to orconcomitantly with the ad dition of an oleophilic colloid theretoenables a greatly increased amount of oleophilic colloid to be added tothe water while maintaining a pumpable mixture. Contacting this mixturehaving an increased amount of oleophilic colloid therein with anoleaginous liquid results in the forming of a stiff gel much morerapidly than is the case when the dispersing agent is absent the mixtureand a lesser amount of oleophilic colloid is necessarily containedtherein. In these laboratory tests, an aqueous mixture was formed byadding grams of oleophilic colloid to I50 ccs of water into which 2grams of chrome lignosulfonate and 1 gram of caustic soda had beenplaced. This slurry was judged to be pumpable and appeared to be lessviscous after mixing had stopped and the sample allowed to stand for aperiod of one-half hour. This slurry was mixed with ccs of diesel oiland a stiff gel was rapidly formed.

Iclaim:

1. In the drilling of a well, the method of alleviating fluid loss intoa subterranean formation penetrated by said well, comprising:

introducing into said well an aqueous mixture of a dispersing agent anda water dispersible oleophilic colloid which acts as an oleaginousgelling agent;

circulating said aqueous mixture down said well and into the vicinity ofsaid formation; and

mixing said aqueous mixture with an oleaginous liquid whereby saidoleophilic colloid is dispersed in said oleaginous liquid and forms agel.

2. The method of claim 1 wherein said dispersing agent is selected fromthe group consisting of lignites, lignosulfonates, tannins, and complexphosphates.

3. The method of claim 2 wherein said dispersing agent is selected fromthe group consisting of chrome lignosulfonates and ferrochromelignosulfonates.

4. The method of claim 1 wherein said oleophilic colloid is a normallywater swellable clay which has been treated to render it oleophilic.

5. The method of claim 1 wherein said oleaginous liquid comprises anoil-base drilling fluid present in said well when said aqueous mixtureis introduced.

6. The method of claim 1 wherein said aqueous mixture is adjusted to analkaline pH by the inclusion of a pH-adjusting chemical.

7. In the drilling of a well, the method of alleviating fluid loss intoa subterranean formation penetrated by said well, comprising:

forming a pumpable aqueous mixture of a dispersing agent and a waterdispersible colloid which acts as an oleaginous gelling agent;

circulating said aqueous mixture down said well and into the vicinity ofsaid formation; and

mixing said aqueous mixture with an oleaginous liquid whereby saidoleophilic colloid is dispersed in said oleaginous liquid and forms agel.

8. The method of claim 7 wherein said pumpable aqueous mixture is formedby adding said dispersing agent into water no later than the addition ofsaid water, dispersible colloid into said water.

9. The method of claim 8 further comprising adding a pH-adjustingchemical to said water to adjust the pH of said water to an alkaline pHand thereby improve the effectiveness of said dispersing agent.

2. The method of claim 1 wherein said dispersing agent is selected from the group consisting of lignites, lignosulfonates, tannins, and complex phosphates.
 3. The method of claim 2 wherein said dispersing agent is selected from the group consisting of chrome lignosulfonates and ferrochrome lignosulfonates.
 4. The method of claim 1 wherein said oleophilic colloid is a normally water swellable clay which has been treated to render it oleophilic.
 5. The method of claim 1 wherein said oleaginous liquid comprises an oil-base drilling fluid present in said well when said aqueous mixture is introduced.
 6. The method of claim 1 wherein said aqueous mixture is adjusted to an alkaline pH by the inclusion of a pH-adjusting chemical.
 7. In the drilling of a well, the method of alleviating fluid loss into a subterranean formation penetrated by said well, comprising: forming a pumpable aqueous mixture of a dispersing agent and a water dispersible colloid which acts as an oleaginous gelling agent; circulating said aqueous mixture down said well and into the vicinity of said formation; and mixing said aqueous mixture with an oleaginous liquid whereby said oleophilic colloid is dispersed in said oleaginous liquid and forms a gel.
 8. The method of claim 7 wherein said pumpable aqueous mixture is formed by adding said dispersing agent into water no later than the addition of said water dispersible colloid into said water.
 9. The method of claim 8 further comprising adding a pH-adjusting chemical to said water to adjust the pH of said water to an alkaline pH and thereby improve the effectiveness of said dispersing agent. 